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Postharvest Handling of Rambutan

The Rambutan (Nephelium lappaceum L) is a perishable fruit requiring careful handling and rapid transport to the market. The fruit's handling and marketing chain normally lasts seven days.

Quality Criteria

Import markets require Rambutan to be fresh in appearance, uniform in color (usually red, but in some cases yellow), at least 2.5 centimeters in diameter, a minimum of 30 grams in weight, and free from blemishes and mechanical damage to both the skin and surface hairs (spinterns). The pulp (aril) should be easily removed from the seed coat and should constitute the major part of the fruit. Varieties that have little aril and/or an aril that remains stuck to the seed coat are not marketable. The aril should be transparent and sweet, with a Brix level of 18o to 20o, and have no off-flavors.

Varieties

Acceptable varieties are those that meet market quality criteria. They also offer growers good yields, adaptability, and disease resistance. Other desired attributes include a long postharvest storage life, resistance to water loss, and resistance to damage during handling operations.

The main cultivars found in top producing countries‹all members of the Association of South East Asian Nations‹are Lebakbulus, Binjai, Rapiah, and Simacan (Indonesia); Gular Batu, Muar Gading, Khaw Tow Bak, Lee Long, and Daun Hijau (Malaysia); Seematjan, Seenjonja, and Maharlika (Philippines); Deli Cheng and Jitlee (Singapore); and Rongrien, Seechompoo, and Bangyeekhan (Thailand). All these cultivars are red when ripe except for Muar Gading and Rapiah, which are yellow. Differences are seen in aril characteristics, postharvest attributes, color intensity, and spintern patterns.

Harvesting

Rambutan should ideally be harvested in the morning or in the late afternoon, when ambient temperatures are lower; harvesting during hot periods can accelerate water loss. Harvesting is carried out every two to three days based on fruit maturity; not all fruits on a tree mature at the same rate. Even among fruits that grow on the same cluster or panicle, maturity is not uniform. Although single harvests are normally preferred, they sometimes result in false economies because variable maturities result in high rejections. The number of harvests per tree in a season can vary from 7 to 20 depending on fruit age and production levels.

Harvest maturity can be judged on a number of factors, but the most reliable is the color of the skin and spinterns.

Fruits are selected for harvest when 80 to 90 percent of the fruits on a panicle are full red‹or yellow for the yellow varieties‹with little or no green color. This is normally 14 to 28 days after color break, or 15 to 18 weeks after fruit set.

Other factors include:

The optimum harvest time varies according to the cultivar. In all cases, fruits harvested too early will not have the required internal quality, as shown with fruits picked 10 days after color break. Over-mature fruits have a very deep skin color with opaque, dry, and very firm arils with poor flavor.

Harvesting is carried out manually using secateurs or pruning shears. The fruits are removed in bunches from the trees, not cut individually, because cutting each fruit is less efficient and increases mechanical damage and water loss. Where harvesting is carried out from the ground, the bunches are placed carefully into plastic field crates. Where ladders are used, the picker places bunches into a cotton bag around his or her waist. This bag should be small, never over-filled, and the fruit regularly and carefully lowered to the ground for transfer to the field crates.

Picking tools can also be used to cut the panicles from tall trees, but these tools should include a bag attached to the pole, so that the fruit does not fall to the ground. A blade, knife, or pruning shears should be used to cut the main stem of the panicle. For transport from the field to the packing facilities, plastic field crates are preferred to sacks, bags, or baskets. Field crates should be shallow, light colored, ventilated, and clean. Damage to spinterns frequently occurs during these handling operations, as a result of dropping, piling excess weight on top of the fruit, and rubbing (fruit to fruit or fruit to container). Damaged spinterns increase water loss and may cause the fruit to turn brown or black, reducing shelf life, appearance, and marketability.

Increases in fruit temperature should be minimized by ensuring crates are not directly exposed to the sun during picking, packing, or transport.

Packhouse Operations

The time elapsed between harvesting and packing should be kept to a minimum. The sooner the fruit is packed and cooled or shipped after harvest, the better the quality upon arrival in the market. Delays between harvesting and packing are frequently the cause of water loss and diminshed quality.

Packing facilities should be arranged linearly and should include a water tank, sponge drying rollers or drying racks, and grading and packing tables. Fungicides are not normally used, although the use of chlorinated water in the wash tank is advisable (100 parts per million).

On arrival at the packing facility, fruits should be cleanly clipped from the bunch with secateurs, leaving 0.5 centimeters of the stem attached. Fruits that are undersized or that show signs of nonuniform color, insect damage and disease, or softening from mechanical damage should be rejected at this point.

It is preferable at this point that the fruits be classified by size and placed directly into the water tank. The water tank should be divided into sections for the different size grades because this system reduces the likelihood of mechanical damage. Tanks should be long and rectangular, rather than square, to allow a constant flow of fruits. Tanks should preferably be made from fiberglass or treated metal rather than concrete; fiberglass tanks cause less mechanical damage, are easy to maintain and clean, and can be moved or expanded as required. To assist with moving the fruits along the water tank, a small stream of water from a pipe on the surface at the tank entry point should be used; the fruits will then move slowly to the exit point as additional fruits are placed in the tank. The rate of fruits entering the tank should equal the removal rate. The fruits need to be in the water for a minimum of 5 minutes and a maximum of 10 minutes. This process is not meant to wash the fruit, but only to remove debris, dust, and insects.

As the fruits reach the end of the water tank, they have to be removed and drained before packing. The process depends on the equipment available. Under optimum conditions, the rambutans are removed from the tank with a plastic crate, to sift and lift fruits collecting on the surface of the water. Sifting helps reduce mechanical damage that may occur when the fruits are placed directly into the crate. The water is allowed to drain, and the rambutans are carefully placed on revolving sponge rollers, passed under high-velocity fans, and then onto a moving belt that directs the fruits to a specific grade table. Because the water tank contains fruits already separated by grade, the drying is carried out on batch basis, with the exits on the conveyor belt being changed depending on the grade. The rambutans can then be packed directly into the cartons.

Where sponge rollers are not used, the fruit must be removed from the tank in crates, and placed on stacked wire mesh trays for drying. Small-mesh chicken wire can be used, but because this can damage fruit hairs, a nylon or plastic mesh with 1.25-centimeter diameters is better. The trays should be stackable, long, and narrow to facilitate loading and removal. Because size grading has already been carried out, different sizes should not be mixed on the same drying rack. Only one layer of fruit should be placed on the drying rack; multiple layers significantly increase the drying time. Under natural conditions, drying can take between one and six hours. Fans may be used to help move air over the racks to assist in drying. Care should be taken to ensure that excessive drying does not occur.

Grading tables should be slightly sloped and protected with a sponge layer and a clear plastic covering. If a moving conveyor belt is used, the tables may be located on either side of the belt. If drying racks are used, the tables should be placed directly behind the drying racks with sufficient space for a person to move fruits from the racks to the tables.

Packing

Fruits should be dry before packing. Separation by variety and by color is normally required, although some buyers may require red and yellow mixed packs. Packing by size is necessary in some markets, normally those for medium and large fruits, but some markets allow mixing provided that the minimum size is met. It is essential to check with buyers to determine size and grading requirements.

Rambutans are packed individually into the carton to ensure maximum use of space; they should not be forced into spaces because force will damage the spinterns. A second layer of fruit is placed on top of the first. The second layer should remain flush or slightly lower than the top of the carton, so that when the lid is closed the fruit is not forced downward. This method of packing also prevents excessive movement and settling of the fruit during subsequent handling and transport.

Carton net weights are two to four kilograms, depending on the importing country and buyer requirements. Some markets prefer rambutans packed in punnets or clamshells, or in trays overwrapped with plastic film. The weight and number of fruits per clamshell depend on the market; one-quart, half-pint, or one-pint clamshells may be used. Packing into these small units aids with presentation, reduces mechanical damage, and, in most cases, extends the shelf life.

Preferred packaging consists of one- or two-piece self-locking telescopic cartons, with a minimum breaking force of 175 pounds per square inch.

Ventilation is required in all four walls. If one-piece cartons are used, the lids should close leaving a maximum space of two centimeters between the fruit and the lid. Carton dimensions vary depending on the net weight and the market. The most common package size is two kilograms with external dimensions compatible with ISO pallets:

If clamshells are used, then compatible flats are required; these too are normally standard sizes and are compatible with the ISO pallets. Packaging should include all the labeling information required by the importing country:

Some research indicates that rambutan color retention and shelf life can be increased with modified atmosphere packaging using plastic bags or wax treatments. These measures have not necessarily been implemented in commercial operations.

Cooling and Storage

Rambutan is a non-climacteric fruit, and although the fruit does show increases in respiration and ethylene production after harvest, this is related to deterioration as opposed to ripening. Ethylene production is normally a stress response, particularly in relation to water loss during storage.

The faster the fruits are cooled, the longer the quality at harvest can be maintained. Storage conditions of 10oC to 12oC, with 85 to 95 percent relative humidity are optimal. Forced air precooling will remove the field heat within 2 to 3 hours if vertical column palletization is used and carton ventilation is compatible; after cooling, the pallets should be placed in a standard cold room. If normal cold room cooling is used, the cartons should be stacked so as to enable air movement around each carton; cooling can take between 8 and 12 hours using this method.

Rambutan should be harvested and shipped the same day. Cooling in this case is not recommended. Cooling is recommended only if the fruit must be held overnight before shipment.

Transport

Rambutan exports are shipped by air. Transport from the packing facility to the airport should be in cool trucks if the fruit has already been cooled. In all cases, trucks should be covered to prevent contact with wind, rain, and sun.

Air shipments are made in aircraft containers or aircraft pallets. Heat build-up in containers is possible, especially if they are left exposed to the sun in the airport while waiting for arrival and loading. Such exposure is obviously harmful to the fruit. Attempts should be made to ensure that the aircraft containers and pallets are kept in the shade or in otherwise cool conditions until loading.

Potential Postharvest Problems

Deterioration is normally manifested by browning of the peel, usually beginning at the point of the spintern and moving toward the base. Quality problems observed in importing markets are normally caused by mechanical damage and poor temperature control, which causes blackening of the spinterns, water loss, poor appearance and discoloration, and subsequent development of secondary fungal infections. Most water loss occurs through the spinterns as a result of the high surface area-to-volume ratio and the presence of lenticels. The prevention of mechanical damage, rapid cooling, and high humidity all reduce the deterioration of the fruit.

If delays are encountered during shipment or if temperature falls below 10oC, rambutans will lose their coloration, become dull, and turn brown. This color is normally associated by buyers with old fruit.

Spoilage caused by fungus can be problematic if there are latent infections from the field, if mechanical damage occurs, or if fruits are exposed to high temperatures and humidity during transport and storage. The disease Botryodiplodia theobromae develops rapidly, spreading dark brown lesions over the whole fruit. This disease normally occurs through mechanical injuries on the cut stem end; it is not latent. Gliocephalotrichum bulbilium is characterized by light-brown water-soaked areas in the skin and the pulp, which can develop yellow mycelia with sporulation on the fruit. Colletotrichum sp. shows similar characteristics to G. bulbilium, although no aerial growth is shown. Both diseases are latent and infection occurs in the field; control, therefore, begins in the field.

Although postharvest fungicide treatments may stop or slow the development of some disease, careful harvesting‹leaving a five millimeter to one centimeter piece of the stem attached to the fruit‹gentle handling, rapid cooling, and storing at optimum storage temperature are more effective ways to minimize disease development.

Sources of Technical Information

Mohamed, S. & Othman, E. 1988. Effects of packaging and modified atmospheres on the shelf life of rambutan (Nephelium lappaceum). Pertanika. 11 (2): 217-228.

Mohamed, S. & Othman, E. 1988. Effects of chemical treatments on the shelf life of rambutan (Nephelium lappaceum). Pertanika. 11 (3): 407-417.

Wong, L.S., Jacobi, K.K., & Giles, J.E. 1991. The influence of hot benomyl dips on the appearance of cool stored lychee (Litchi chinensis Sonn.). Scientia Horticulturae. 46 (3-4): 245-541.

Zauberman, G., Ronen, R., Akerman, M., Weksler, S., Rot, I., & Fuchs, Y. 1991. Postharvest retention of the red color of litchi fruit pericarp. Scientia Horticulturae. 47 (1-2): 89-97.

SUMMARY SPECIFICATIONS FOR RAMBUTAN EXPORTS
VARIETIES:	See box on page 8 for list of most common cultivars found in main producing nations. Acceptable cultivars should meet market specifications, have a long postharvest life, and be resistant to water loss.
SIZE:	Minimum weight 30 grams Minimum diameter 2.5 centimeters
COUNTS:	Counts will vary depending on carton size and size of fruit.
PACKING:	Fruit typically packed by variety, color, and size, although some importers may require red and yellow mixed packs, or packs of varying sizes provided the minimum size specifications are met). Carton weights vary between 2 kilograms and 4 kilograms. Some importers may require pre-packed rambutans (in punnets, clamshells, or trays overwrapped with plastic film).
CONDITION:	Fresh in appearance, with no signs of insect, disease, mechanical damage, softening, or surface dirt and debris Uniform red or yellow color, with little or no green, and no brown or black spots Aril that is easily removed from seed coat, is transparent and sweet, has a Brix level of 18o to 20o and no off-flavors, and constitutes the major part of the fruit Free from blemishes and mechanical damage to both the skin and surface hairs (spinterns) 0.5 cm of stem attached
STORAGE:	10oC to 12oC, 85 to 95% relative humidity optimal
NOTE: Importers¹ specifications vary by importer and market. Exporters should check with importers regarding their specifications prior to shipment.

Cultivar	Color	Country of Origin
Bangyeekhan	Red	Thailand
Binjai	Red	Indonesia
Daun Hijau	Red	Malaysia
Deli Cheng	Red	Singapore
Gular Batu	Red	Malaysia
Jitlee	Red	Singapore
Khaw Tow Bak	Red	Malaysia
Lebakbulus	Red	Indonesia
Lee Long	Red	Malaysia
Maharlika	Red	Philippines
Muar Gading	Yellow	Malaysia
Rapiahs	Yellow	Indonesia
Rongrien	Red	Thailand
Seechompoo	Red	Thailand
Seematjan	Red	Philippines
Seenjonja	Red	Philippines
Simacan	Red	Indonesia

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Postharvest Handling of Rambutan

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